Even if I’m not expressly fasting, I gravitate towards working out on an empty-ish stomach. It just feels right to me to run on empty or, at the most, a couple eggs or a handful of nuts. Lifting heavy things while picturing the pounds of meat to come is, for lack of a better word, kinda Primal. The hunger fuels my performance – at least it seems to – while a brick of food sitting in my belly is a subjective burden. Look around the blogosphere (especially at Leangains and Free the Animal, where Martin Berkhan and Richard Nikoley have been doing some great work together charting Richard’s Leangains journey) and you’ll see that plenty of others are feeling the same.

What’s cool is that research in objective support of this stuff keeps coming. Earlier this week, the NY Times highlighted a Fall 2010 study that Martin broke down back in September. Both covered it quite extensively, and while I prefer Martin’s take on it, I also like that working out on an empty stomach is actually being recommended in a mainstream publication like the Times. They don’t even include the normal caveats from stuffy experts.

This particular study took lean, active young 20-something men and broke them up into three groups: a fasted training group, a fed training group, and a non-training control group. The fed and fasted groups ate the same meals made up of the same foods, just at different times relative to the workout. They both trained in the morning, a mix of hard endurance stuff, lots of glycolytic work. No weights. The fasted group destroyed the fed group. All groups were eating an isocaloric high-fat, high-carb (50/40/10 F/C/P) diet well above maintenance, but the fasted group gained the least weight and the least amount of body fat. Most importantly, glucose tolerance and insulin sensitivity improved in the fasted group and suffered in the fed group (you don’t even wanna know about the poor control group), meaning the fasted folks were better able to shuttle nutrients into their muscles and handle both carbs and fat together. I can’t imagine the food quality was doing them any favors, either; Martin notes that subjects were supplied with take home meals, which I read as processed, boxed crap full of frankenfats and refined grains.

There’s more, of course. A study released earlier this month describes the beneficial effect of fasted endurance training on post-workout eEF2 activity. eEF2, or elongation factor 2, is a crucial factor in muscle protein synthesis. eEF2 is subject to either dephosphorylation (generally good for protein synthesis) or phosphorylation (generally inhibitory of protein synthesis). Subjects were split into two groups: CHO, who received a carb-rich breakfast before and carb-rich drinks throughout an endurance training session; and a fasted group, who received only water. Training was 3x a week for 2-hours at 70% VO2 max for both groups (not my cup of tea, personally). The CHO and fasted groups both had comparable eEF2 phosphorylation pre workout, but post workout, CHO group phosphorylation doubled and dephosphorylation was largely negated, while fasted group dephosphorylation was maintained and phosphorylation remained stable. Remember: dephosphorylation good for muscle maintenance, phosphorylation not so good. As I’ve said before, this type of endurance training can be fairly catabolic, and I myself had trouble maintaining weight, let alone actual muscle mass, as a runner.

Another study seems a bit more mixed. It looked at sprinting athletes, either fed (24g whey protein, 4.8g leucine, 50g maltodextrin/glucose) or fasted and then told to sprint. Power output and performance were similar, but fed athletes displayed greater muscle protein synthesis and muscle cell signaling. From what I can tell, though, the fasted athletes were never fed, not even after the sprinting. This is definitely interesting, but I’d like to see what happens to fasted athletes who eat right after training. The study’s authors even conclude that the important thing is ingestion of carb/protein in “close proximity” to time of training irrespective of chronological order.

The takeaway? It’s just more fuel for the fire. Fasted training improves metabolic performance and helps maintain muscle after endurance exercise, and, as long as you eat soon after, can jibe with intense sprint work. I’ll continue covering this topic as new research is unveiled. Stay tuned.

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

It’s nice to see some actual studies on this topic. I looked into Leangains before, but couldn’t really tell any difference in increased strength or anything. I think, I couldn’t really get over the idea that it seemed like the guy was just marketing “skipping breakfast” as “intermittent fasting”. Keep the studies coming, though. I’m definitely willing to give it another shot if it is backed by science

Let me rephrase…yes the author of Leangains cites scientific sources all over the place. There are scientific sources that can support any hypothesis in the world (including that skipping breakfast is detrimental). He seems to be knowledgeable, and I’m not knocking whatever works for him, and whoever else likes it. I’m saying that for me, I didn’t notice anything spectacular about training fasted, but I will continue looking at all the research (not just the research that supports whatever hypothesis I’m following at the moment), and am definitely willing to change my strategy if I can find sufficient reason to do so.

I have looked at the Leangains site too, and it isn’t just about “skipping breakfast”. Fasting (for Martin) means not eating for 16 hours and then to be in the “fed” state for only 8 hours. There is much more to it as far as what to eat to break the fast and what to eat on training days vs rest days, but in essence it’s about putting your body in a fasted state which requires more than just skipping breakfast.

How did the study keep the base performance ranges of the three groups as close to each other as possible? I.E. not segregating Crossfit champions into group “fasted”, couch potatoes in group “meal beforehand” etc?

Also how long of a duration without food is “fasted”? It would be interesting for the researches to see how long before the benefits of fasting are eclipsed by the negatives of starvation.

This study flys in the face of everything I have perceived from my own body. I can barely make it through a 25 minute metcon as it is. Hard to believe that forgoing my 1/2 yam + 2 eggs an hour before hand would be *aiding* my cause o_O. I’ll tinker with a fast and see how I perform.

Before I became Primal (a year ago) I could never train fasted, in fact I awoke starving hungry and HAD to eat before heading out for training of any description.

However, now, I prefer to train fasted although before a longer session – ie a long bike ride I would have a breakfast of eggs and bacon first. But for other sessions fasting is good. I often combine an IF with the following protocol eat around 7 pm, then nothing, a herbal tea on awakening and then in the pool at 7 am for an hour’s session (easy plus some sprinting), into the gym for weights workout, sometimes the 1-2-3 WoW and very often not eat until 4 – 5 pm.

Works beautifully and my improved performances would suggest my body likes it. I would not however try chronic cardio sessions or schedule a really heavy session within 12 hours of eating again as you just trigger the carb monster in my experience, but allow your body to natural refuel itself and you stay strong and lean.

It seems like the main takeaway from these studies is to eat sometime in the general vicinity of a hard, muscle-building workout, if you’re looking for gains. Everything else, at least listening to folks’ anecdotes, seems to be personal. I hate trying to work on an empty stomach, although I do give it time to digest. My SO, on the other hand, insists that she feels heavy and slow when trying to work if she’s eaten within a couple hours before a workout.

Could the nature of the workout be a factor, too? Sprinting or weightlifting versus endurance or distance?

I do more of an Eat-Stop-Eat style of fasting (24 hours, 1-2x per week, very flexible). This typically means I eat dinner one night, then fast until dinner the next night (on random mornings where I’m just not hungry…happens about 1-2x per week naturally!).

I’m wondering what I’m missing out on with training in the morning on those days. Like, if I wake up and work out (ALWAYS fasted), and then fast all day, am I missing out on muscle building? Does it matter? If I ate tons of protein the day before, I understand that there will be amino acids trickling into my bloodstream for quite some time after…so do I really need to eat after? Better phrased: Is it in any way beneficial to eat right after? Or can I wait until dinner?

I still have lots of muscle, and I’ve been doing this for a year. Looking for thoughts!

I know for me, going to Rugby practice or game time with food in my stomach, it would be right back up again in a few minutes. I enjoyed the feast afterwards, albeit back then it was beer (when your sponsor is Miller light you have to drink it!) and sandwiches/pizza/wings/everything.
Today, I really enjoy my workouts in the fasted state because I feel the workout (pain). my fasted states are longer now than before, but I think that helps more.

I’m glad you wrote about this article, Mark. I was very interested in it as well, since usually I do a couple of laps of my local pool early in the morn before breakfast and I always feel great by the time I eat. Nothing strenuous though. Definitely better than eating than swimming with a tum full of food and dealing with cramps. My bub loves it too (in the belly) she kicks and rolls around while I swim…At least I think she likes it lol, she could be freaking the hell out!

I Hunt! There, I said it. OK? I know some are against it but its what I do and part of who I am. I also fast prior to hunting. Maybe I am more focused, maybe I smell less human or mayby I just try harder…I dont know. But i dont eat the morning of a hunt and like it was stated “it feels more primal”.

facinating, I always played my best games on an empty stomach. Frank Leahey, the coach for Notre Dame in the 50’s, always had his players litteraly play hungry. This was way before the steroid era, He lost a couple of games in four years. Makes sense, when I’m hungry and not in the mood for niceties, probably a genetic trait that makes us willing to go hunting.

I’ve always performed better with sprints and other high intensity endeavors in a fasted state. And I’ve found my hunger is better regulated post-fasted intervals. Not to mention when I do eat post-workout I feel like I’ve earned it!

I’ve started IF about 3 months ago, and I have to say that my workout has improved immensely.
I stop eating about 6pm, and don’t eat again until around 11am the next morning. I work out for about 1-2 hours in the morning in a fasted state. The only thing I recommend is to drink lots of water preworkout. It also helps if you feel hungry.
On mornings if I do eat something before my workout, I definitely feel much more sluggish. I make an effort to not eat beforehand.
I have also noticed that even though my weight has basically stayed the same, My clothes are looser and I can only attribute that to fat loss and muscle gain.
I can’t recommend intermittent fasting highly enough.

I seem to perform best on a small amount of food prior to training if I’m doing cardio. It was 18 degrees F this morning in Chicago, so I ate mostly fat for breakfast (some bacon and sausage) about 1 hour before going for my run.

I seem to be able to lift weights or do body weight routines in a fasted state.

Since I have started working out in a fasted state my energy levels get better the more the work out progresses. I never had this before when following the protocol of eating every 3 hours. I usually ended up feeling letahrgic because of the food in my stomach????

I have been fasting for almost 3-4 month 3 times a week 20-22 hrs and do my work out one in the morning (body weight strength) one at the end of the day (sprint-intervals). i feel much better ; at 5 pm i feel a little hungry but when i start exercising i dont realize how the time goes by and i perform better;;feel lighter..stronger and more concentrated whatever i am doing.

Great article!! Love it! Thriving on vegan veggie strong -nonprocessed-no grain fuel…However, I follow MDA for the articles:) Nice to see research on fasting states and physical exertion. I have practiced early morning long distance running (10-15mi) on a fasted system and that feels spot on for my body!! Currently, doing Crossfit workouts mid-morning… I still find less is more. However, I feel compelled to eat something as I am nursing an infant through the night.

Don’t mind. Vegetables have protein!!! I LOVE and eat ALOT of vegetables and a good variety of them. I eat fruit too. I eat a WIDE variety of nuts and seeds…I don’t just stick to a few. I eat a variety of beans…no tofu or processed soy only whole soybeans. I supplement with raw hemp protein and pea protein. I guess there’s a little processed food in the mix as Spirulina, dulse and almond milk add a nice touch here and there. For me variety is key:) I have two healthy boys and with the last pregnancy was hitting the gym 6-7 days a week doing intense workouts up to the day of birth….no problemo. And I am animal when it comes to athletic competition. It works for me.

I’ve heard this go back and forth a number of times in the last year. Here is a Modern Paleo article (admittedly without much scientific backing), that speaks glucoeneogeneis and the release of cortisol:

I think this definitely varies from person to person and I would suggest anyone with cortisol issues get that under control first before introducing anything that might produce more cortisol, even if it is only speculation.

For me, I do the De Vany thing and train fasted when it’s weights. If I know I’m going to go catabolic (sprints, metabolic conditioning, etc), I try to make sure there is something in the tank.

If I’ve read this correctly, it seems the carbo-loaded fed group did worse than a fasted group, but when the fed group had protein, they did much better that the fasted group. If so, is it really fasting that is causing the improvement, or is it cutting out carbs?

I’ve noticed that sometimes I do feel much better working out when I haven’t eaten in awhile, but the caveat seems to be that it only extends to a certain amount of time. If I haven’t eaten in 10 hours my performance seems to suffer significantly.

HOWEVER, I haven’t pinpointed it precisely yet, though and it could have also been other factors–not drinking enough water–not enough fats the previous day–etc.

love working out fasted, but for one thing. deads. when i have nothing in the tank, i feel like i am going to pass out after a heavy set. i googled this, seems fairly common. so, i am thinking that a handful of nuts prior to hitting the gym on back day will help- hope so, anyway.

Interesting that the authors don’t “trust” self-reporting in the early stages of the study because the control group didn’t gain as much weight as expected, and so increase all subjects intake 500 kcal/day. However, when the fasted exercise group gains less weight when compared to the CHO group, the fact that maybe they under-reported and ate less didn’t cross their minds. This has to be considered as a possibility!

Also, exercise intensities were matched between groups such that CHO’s workload were matched to F’s intensity. What if CHO could have performed more work to achieve a similar intensity?

No studies on women. I’ve done fasted workouts, workouts 1hr post normal meal, and workouts with 100-200 calories on board. Since this is n=1, no conclusions, but I’d have to think the difference in hormone types and levels has some bearing on fat gain/loss, muscle gain/loss, and general well-being, yes?

It’d be interesting to see the same study on women, yeah. I absolutely can’t run without having some food 30 mins to two hours before. I also can’t run if I’ve just eaten – there’s definitely a sweet spot. Looking at the comments I seem to be alone, but I’ll stick with eating – getting lightheaded, dizzy and feeling like my tank is empty aren’t fun!

I would be interested in seeing a study about women as well. I never used to think there would be a difference, but many recent studies that were redone for just women has changed my mind. There can be major differences or it can be exactly the same, and you never know until the study is done. although I for one don’t like eating until a couple hours after I wake up, it is more comfortable for me personally. We’ll see how I feel when I add workouts to my mornings.

Some fascinating studies that look at men and women ultra distance runners (not fasted as far as I’m aware – although with ultra you are pretty much in a semi-fasted condition I suppose) but they show that the metabolism between the genders is different to the extent that women out-perform men once you get to the longer distances it seems to be to do with metabolising fats and where those fats are stored.

This is definitely interesting. I am also interested in other studies of women. I have tried both fasting and eating before a workout. If I do eat, it has to be a few hours before the workout, especially if it involves cardio, or I tend to get dizzy and pass out. I can also be the same if I have fasted. I am fairly thin, so do not have much fat storage. When I was younger I was definitely good with the long distances; I could just keep going.

Kitty wrote on December 22nd, 2010

On a Paleo diet I find my energy levels are nice and constant so I don’t have to worry about insulin spiking and making me tired before a workout. But I don’t go eat a giant steak right before a squat workout!

That being said I compete in strongman and need to be big. Fasting doesn’t exactly fit into those plans.

It sounds to me like the leangains guy really has named skipping breakfast fasting. Most people fast 10-12 hours a day without even trying. Then, there’s those who skip breakfast because they’re too lazy to get food ready that early. To refer to the times when you finally get around to eating as the “fed state” is really pushing it. This guy is a genetic freak of nature and quite possibly a descendent of P.T. Barnum.
If you’re going to fast, then fast. If you’re going to skip breakfast…

β-HYDROXYBUTYRATE: THE MOST EFFICIENT FUEL Veech and colleagues discovered that administering β-hydroxybutyrate to the perfused rat heart in place of glucose increased work output but decreased oxygen consumption (35).

“Looking at real world examples, the Kenyans, hailed for their superior endurance in running events, are known for doing a brunt of their training in the fasted state. They also follow a high carb diet to maximize muscle glycogen storage. According to experts, this pattern of “training low” and “competing high” might provide a distinct advantage. Muscles that are well stocked with glycogen can simply outwork the competition.”

If you have found success with intermittent fasting, then awesome – keep it up…but to suggest that it has been proven conclusively better than training in fed state (Or that anyone with a different point of view is an idiot), is extremely narrow-minded. I expect people on this site to be more open about things.

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